A 20-year-old woman who police say was seriously drunk Saturday morning caused a head-on crash in Santa Rosa that injured three generations of one family in another car.

Shannon Hullinger of Santa Rosa's blood-alcohol level was 0.20 percent, more than twice the legal limit for driving, police said. She also is below the legal drinking age of 21.

Hullinger sustained minor injuries in the 10:30 a.m. crash on Highway 12 near Melita Road.

At the hospital, the investigating officer determined Hullinger was intoxicated and had her blood tested, Sgt. Lisa Banayat said.

Hullinger was subsequently arrested on suspicion of drunken driving and booked into Sonoma County Jail. Her bail was set at $100,000, jail personnel said.

Banayat said multiple callers reported a Nissan Sentra had overturned in the westbound lanes of Highway 12 with people trapped inside.

Santa Rosa firefighters were able to free the trapped driver, a 77-year-old grandmother from Boyes Hot Springs. She suffered a fractured neck and was hospitalized, Banayat said.

Her daughter, a 26-year-old Sonoma woman, was treated and released with abrasions and other injuries.

That woman's 4-year-old child, who was in a booster seat in the back of the car, suffered a broken arm and was also released from the hospital.

Their names weren't available Saturday night.

Based on evidence at the scene, witness statements and video from a nearby 7-11 convenience store, Banayat said investigators believe Hullinger's Ford Mustang was eastbound Highway 12 when it crossed the center divider and collided head-on into the Sentra, causing the smaller car to flip onto its roof.

Three ambulances transported the four victims to local hospitals, Banayat said.

The roads were closed until 12:45 p.m. while police investigated.

Police ask any witnesses to call 543-3600.